No no no no no no no, you are so very, very wrong.
You CANNOT increase your maximum heart rate, your maximum heart rate is the rate that your heart can achieve, but cannot exceed.
Saying your MHR was 175bpm when you started shows you just how wrong the calculation was.
Your heart rate can never go "too high", you will reach your maximum, and thats it, of course, having your heart rate at your maximum for too long isn't a good idea, but you'd probably hit your lactating threshold and physically not be able to do anymore before your heart packs in, unless you are obese or extremely unfit.
Your MHR does decrease with age, but everyones MHR is personal to them, and the theoretical calcs are a waste of time for the majority.
I have lost count of the amount of people who use HR based training and never found out their true MHR, any HR based training based on theoreticals is pointless.